Low Poly Art Deep Zoom Animation
You can create a high-poly mesh and animate the collapse ratio of its decimate modifier to reduce the polycount while the camera is zooming out.


Original Mesh



Mesh with decimate ratio of .016.
Learn more about the decimate modifier here: https://docs.blender.org/manual/de/dev/modeling/modifiers/generate/decimate.html

As for leaves, I'm not sure. It's hard to do a seamless transition between a bunch of individual leaves and a solid "block" you'd see in most low-poly renders.